1. Field of the Invention
The present invention relates to improved processes to prepare camptothecin derivatives, such as irinotecan, in a one-pot operation.
2. Description of the Related Art
Camptothecin 1 (shown in FIG. 1A) is a pentacyclic alkaloid that was isolated by Wall et al. in the early 1960s from the Chinese tree, Camptotheca acuminate (Nyssaceae). The compound raised immediate interest as a potential cancer chemotherapeutic agent due to its impressive activity against a variety of tumors. However, a shortcoming of camptothecin as an anti-cancer agent was its poor solubility in water. To overcome the solubility problem, the sodium salt was synthesized by hydrolysis of the lactone ring. The sodium salt forms an equilibrium with the ring-closed lactone form. As its sodium salt, camptothecin was moved to clinical trials and promising activity was initially observed. However severe side effects and drug-related toxicities finally led to discontinuation of the clinical program.
Stimulated by the challenging structure and its very interesting biological activity, synthetic approaches to camptothecin were developed. During semi-synthetic and total-synthetic chemistry programs, the particular importance of the lactone ring and the C20 (S)-configuration for good biological activity was recognized. In contrast, modifications in the A-ring and B-ring, particularly in the C9, C10 and C11 positions, were tolerated and led to improved analogues.
Second-generation camptothecin derivatives have been optimized for improved water solubility to facilitate intravenous drug administration. Highlights resulting from various programs at different companies and institutions are irinotecan 2 and topotecan 3, two compounds which are successfully used in clinical practice, and SN-38 4, exatecan 5, liposomal lurtotecan 6 (OSI-211) and CKD-602 7, which are in advanced stages of clinical development. The chemical structures of these compounds are shown in FIGS. 1A and 1B.
SN-38 is a camptothecin derivative that contains a hydroxyl group at the C10 position and an ethyl group at the C7 position. Irinotecan is a camptothecin derivative (it may also be viewed as a derivative of SN-38) that contains a sidechain at the C10 position and an ethyl group at the C7 position. Irinotecan was discovered at Yakult Honsha and was first approved in Japan in 1994 (Camptotesin®) for lung, cervical and ovarian cancer. Today it is marketed in the U.S. by Pharmacia (Camptosar®) and by Aventis in Europe (Campto®). Irinotecan is a prodrug which is cleaved in vivo by carboxylic esterases, particularly by hCE-2, to release the active metabolite SN-38.
The synthesis of irinotecan has been described in the chemical literature and in patents. A common approach to the synthesis of irinotecan is to form SN-38 and then add a sidechain to the C10 position of SN-38, to thereby form irinotecan. U.S. Pat. No. 4,604,463 is one example of a patent that describes this approach, wherein either an activated form of the sidechain is separately formed and then reacted with SN-38, or the C10 hydroxyl group is activated and then in a separate reaction the sidechain is added.
Although there have been advances in the field, there remains a need for improved methods to form irinotecan from SN-38. The present invention addresses this need and provides further related advantages.